Alloimmunization against histocompatibility antigens occurs in 30-50% of patients with acute non-lymphocytic leukemia and can comprise the delivery of potentially curative post remission therapy. There are a number of potential means of decreasing this incidence, the relative merits of which are discussed in this grant proposal. The University of Maryland Cancer Center (UMCC) is interested in and prepared to participate in randomized clinical trials to compare these various modification of transfusion practice to the standard approach of pooled platelet concentrates from random donors. The UMCC is an excellent environment in which to conduct such studies for the following reasons: (1) there is a well-documented availability of 30-40 new patients with acute non-lymphocytic leukemia suitable for study/annum; (2) the same investigators are responsible for the leukemia and transfusion services guaranteeing a high degree of compliance and randomization; (3) the UMCC has conducted and published multiple studies in the area of transfusion supportive care and platelet immunology; these have included a number of randomized studies, one of which was a randomized trial using leucocyte depleted platelets to modify the rate of alloimmunization; (4) the UMCC has extensive experience in cooperative cancer treatment groups and has facilities for and years of experience with collection and transfer of research data; in addition the UMCC currently enters all platelet transfusion results into a computerized data base used for clinical and research purposes and potentially adaptable for use in this RFA; (5) both investigators on this proposal have chaired and analyzed national group clinical treatment trials and the P.I. currently chairs the Leukemia Committee of the Cancer and Leukemia Group B. A subcontract with the Baltimore Rh Typing laboratory to serve as a reference laboratory to perform lymphocytotoxic antibody screens is submitted as a supplement to the UMCC proposal.